1. Field of the Invention
This invention relates to a pneumatic belted tire provided with a belt reinforcement serving to reinforce a tread on a crown region of a carcass, and more particularly to an improvement of a pneumatic belted tire for use in motorcycles.
2. Description of the Prior Art
In general, a pneumatic belted tire of this type mainly comprises a toroidal carcass of radial or semi-radial structure composed of one or few rubberized plies containing cords arranged in a direction perpendicular to the equator of the tire, i.e. a plane including a mid-circumference of a crown region of the carcass or at a certain inclination angle close to the above direction, and a belt superimposed about the crown region of the carcass and composed of two or more rubberized layers each containing inextensible cords such as steel cords or the like arranged at a small angle of not more than 30.degree. with respect to the plane including the equator of the tire, the cords of which being crossed with each other. Moreover, tires having the same belt structure as described above even when the carcass has a so-called bias structure may be included in the belted tire.
These belted tires have hitherto been developed for exclusive use in four-wheeled vehicles and restricted to the applications for such vehicles. In this connection, the equatorial plane of the tire is always held at a substantially vertical state with respect to the ground surface while running, so that the tire tread always comes into contact with ground over its whole width. Hence the belt is located in parallel with the ground contact surface over its width. As a result, the belt having a remarkably high rigidity is located just above the ground contact area over the entire circumference of the tire, so that the belted tires are particularly superior in the cornering stability, wear resistance and so on. It is widely known that the radial tires exhibit a good ride comfortability owing to the peculiar cord arrangement in the carcass ply. Therefore, almost all bias tires widely used have been replaced by the radial tire at present.
On the contrary, when a motorcycle is subjected to a cornering (or a turning movement) in the running, a unique operation mainly depending upon a so-called camber thrust is added, which is entirely different from the case for the four-wheeled vehicle. Moreover, the camber thrust acts as a centripetal force to the ground contact surface of each of front- and rear-wheeled tires, which is opposed to a centrifugal force produced in a body of the motorcycle when the motorcycle body is inclined toward the cornering side in the cornering.
If the radial-structure tire for use in the four-wheeled vehicle is applied to the motorcycle, the camber thrust is very small as compared with the bias-structure tire because the sidewall is extremely flexible. Particularly, when the motorcycle body or the tire is inclined in the cornering, the camber thrust to be produced in accordance with a camber angle or an inclination angle of the equatorial plane of the tire with respect to a vertical line drawn from the road surface cannot smoothly be produced because the difference in the rigidity between the tread reinforced with the belt and the sidewall is excessive. Therefore, there is taken no notice of applying the conventional radial-structure tire to the motorcycle up to now.
The inventors have found that the belted tire can effectively be adapted to the application for motorcycles by reinforcing a predetermined region of the sidewall and a crown region of the carcass with well-known means such as hard rubber and/or cord layer, respectively, and further adopting a proper means for the prevention of cracks, which are apt to occur in groove bottom of a pattern formed on the tread surface due to the specific cord pass of the belt based on the fact that the tread in the motorcycle tire originally reaches near to the position of the maximum width of the crown region, to the belt superimposed about the crown region.